Direction-of-arrival (DoA) estimation is required in many contexts, such as mobile communications, radar, and satellite communications. The information it provides can be used for localization purposes and for radio channel modeling. DoA estimation systems can use amplitude and/or phase information from an antenna or from an array of antennas to determine the direction from which a radio signal originates.
The publication “Direction-of-arrival estimation method based on six-port technology” by S. O. Tatu et al, IEE Proc.-Microw. Antennas Propag., Vol. 153, No. 3, June 2006, p. 263-269, in particular, presents a laboratory demonstration of DoA determination using a technique referred to as phase interferometry. More specifically, a phase interferometer uses a waveguide structure referred to as a six-port junction, comparable to the one shown in FIG. 1, for phase discrimination. In this configuration, two antennas are spaced apart from one another in a detection plane by a separation distance, and the difference between the detected phases of the signal between the two antennas is used to determine the DoA (in two dimensions, within the detection plane). A higher separation distance in the system can lead to a higher angular resolution. However, separation distances larger than the wavelength of the impinging signal can lead to ambiguities due to a phase wrap effect. This phase wrap effect is due to the nature of the phase difference of the signals received by the system, and depends on the ratio between the wavelength λ of the detected signal and the distance L between the receiving antennas. For L/λ 0.5 the complete half-plane DoA range is covered by the range of Δϕ. This leads to a non-ambiguous DoA detection. For L/λ>0.5, the phase will wrap within the chosen DoA range thus leading to ambiguity.
While this demonstration was satisfactory to a certain degree, there remained room for improvement. Particularly in terms of developing a technology to allow manufacturing at an industrial scale and at a satisfactorily low cost. For instance, in order to position the antennas sufficiently close to one another, additional transmission lines were required between the antennas and the input ports and these were undesirable.